1. Technical Field
The present invention relates to a liquid crystal display device, more particularly to a liquid crystal display device which provides a seal member for sealing periphery portions of two substrates, and a method of fabricating the same.
2. Prior Art
An active matrix liquid display device which uses a thin film transistor, comprises a TFT array substrate in which gate electrodes (Y-electrode) and data electrodes (X-electrode) are arranged in the form of a matrix and thin film transistors (TFT) are disposed at intersecting points of the matrix, and an opposite substrate located so as face the TFT array substrate with a gap there between. By the thin film transistor, the liquid display device controls a voltage applied to a liquid crystal which is sealed between the TFT array substrate and the opposite substrate, and can performs an image displaying utilizing an electro-optic effect of the liquid crystal.
A seal member has been generally employed to seal a liquid crystal between two substrates made of glass or the like, which serves to guard the liquid crystal from contamination due to such as water from the outside of the device and environmental changes. This seal member is mad of thermoset resin and ultraviolet-curing resin, and formed on a periphery portion of one of the two substrates, using a painting method by means of a screen printing or a dispenser. The other substrate is adhered to one substrate on which the seal member is formed, and then both substrates are pressed to each other while heating them. In the case of the ultra-curing resin, the ultra-curing resin is cured. Thus, both substrates are joined by the seal member. Properties showing low curing temperature and free from contamination for the liquid crystal due to curing agent, besides a high mechanical adhesion strength and a high stability for environmental changes in temperature and humidity, are required for the seal member.
As background arts concerning the seal member, technologies for constituting the seal member to a double structure are disclosed in the following gazettes. For example, in Japanese Patent Laid-Open No. Sho 57(1982)-171319, notches are provided in an inner seal member of the double structure, whereby a seal width contributing to a gap regulation is made to be large. In Japanese Patent Laid-Open No. Hei 5(1993)-5890, a corner portion of the inner seal member is broken, whereby air traps, which are hollow portions created by entering of air to a place to be originally filled with the liquid crystal, is made not to be produced in the liquid crystal in injecting the liquid crystal into the double structure. Moreover, in Japanese Patent Laid-Open No. Hei 5(1993)-127177, a plurality of openings are provided in the inner seal member, whereby the liquid crystal is injected into the double structure in a short time without damaging an alignment film. In Japanese Patent Laid-Open No. Sho 64(1989)-54420, an opening portion is provided in an inner seal member, whereby a sufficient amount of a liquid crystal can be injected into an area of the inner seal member.
Furthermore, in Japanese Patent Laid-Open No. Hei 5(1993)-232482, a wall portion made of a metal wiring material is formed in a liquid crystal injection port of a single circular seal member so as to make a flow direction of the liquid crystal unchanged, thus preventing an occurrence of alignment disoderedness and defect of alignment.
Although the following technology does not directly relate to the present invention, a technology, in which an outer periphery for connecting a refection plate and a liquid crystal cell is buried with a seal member and double projections are provided inside of the seal member, is disclosed in Japanese Patent Laid-Open No. Sho 62(1987)-286018.
As described above, there are many background arts concerning the seal member. All of these background arts technologies which can be adopted when an area that is a periphery of the display area in the liquid crystal display device can be sufficiently secured. However, owing to a demand for miniaturization of the liquid crystal display device in recent years, the frame area around the display area, which is as narrow as 2 to 3 mm, must be designed. The two substrates are pressurized and heated after the two substrates are laid on top of another, so that the seal member f-lows out partially in a fluidized state. In the case of the narrow frame, the seal member sometimes spreads into the display area via wirings. Particularly, since mixed resin is used for the seal member, a flowing-out speed of the seal member differs depending on a difference in materials, and the spread of the seal member is not straight. As a result, since the seal member spreads out in a melted state while producing meanders, an area that projects significantly from the frame partially occurs. The display area in the liquid crystal display device is constituted so that the liquid crystal is ordered by an alignment film so as to be arranged correctly. If the seal member spreads into the alignment film, a thin film made of the seal member is, for example, formed on the surface of the alignment film, and the alignment of the liquid crystal is disordered. Furthermore, in the case of a normally-white mode in which upon application of a voltage, a displayed image becomes black, the portion of the display area where the seal member spread remains white in spite of the application of the voltage. Hence, there is a problem that a defective display occurs.
The present invention was made to solve such problems, and the object of the present invention is to provide a liquid crystal display device which is capable of preventing a seal member melted from flowing out into a display area.
Another object of the present invention is to provide a liquid crystal display device which is capable of preventing a defective display owing to generation of air traps in injecting a liquid crystal into a gap between superposed substrates.
Still another object of the present invention is to provide a liquid crystal display device which is capable of preventing a cell gap from being different partially from each other, which is a gap between superposed substrates.